1. Field of the Invention
The present invention relates to a thin-film magnetic head which is suitable for an external magnetic storage unit of a computer system and the like.
2. Prior Art
Conventionally, in order to raise S/N ratio of a reproduced signal, number of coil conductors of the magnetic head is required to be increased. However, when sufficient number of the coil conductors are to be embedded in one layer, length of a core should be elongated so that a writing/reading efficiency is deteriorated. For this reason, the prior art employs a multilayer structure for making the coil conductors in general.
FIG. 1 is a sectional view showing the conventional thin-film magnetic head, wherein the coil conductor is constructed by four layers. In FIG. 1, 1 designates a lower core formed by an alloy material such as Ni-Fe alloy, and 2 designates a gap layer. This gap layer 2 is formed by forming Al.sub.2 O.sub.3 film (i.e., alumina film) or SiO.sub.2 film (i.e., silicone oxide film) based on sputtering method. This gap layer 2 forms a gap G of a thin-film magnetic head H. In addition, 3 designates an insulating layer which is formed by heating a resist for 30 minutes at a temperature of 230 degrees Celsius. Further, 4a designates a first coil conductor layer which is spirally formed on the insulating layer 3; 4b designates a second coil conductor layer; 4c designates a third coil conductor layer; and 4d designates a fourth coil conductor layer. Furthermore, 3a, 3b, 3c, 3d designate insulating layers which respectively insulate and coat the above-mentioned coil conductor layers 4a, 4b, 4c, 4d. 5, 6 designate upper cores each of which is formed by Ni-Fe alloy material.
Then, an edge portion of the thin-film magnetic head (left in FIG. 1) is formed by sandwiching the insulating layer and gap layer between the lower and upper cores. "A" in FIG. 1 designates an edge position of the insulating layer 3, and this edge position A is called "zero throat height position", i.e., this is a position where a throat height is zero. Such throat height, namely gap depth, is a distance from the edge position A to the edge B of the upper and lower poles of the cores. If the throat height deviates from the designed value, the magnetic efficiency of the magnetic head will be significantly deteriorated.
Since the above-mentioned thin-film magnetic head as shown in FIG. 1 has the multilayer structure, the insulating layer 3 is easily affected by the process of forming the upper layers on the insulating layer 3. Particularly, since the resist which forms the insulating layer 3 is made by organic material, the resist is easily affected by resist stripper or ion-milling process to be executed when forming the coil conductor layers 4a-4d. Thus, the edge position A of the insulating layer 3 having important functions as determining the throat height which is a distance from the edge B of the poles may be partially eroded by some micro-meters. In addition, surface of the insulating layer 3 becomes rough or partially peels from the gap layer 2. For such reasons, the edge portion can neither be formed in the designed scale nor in the designed position, which deteriorates the writing/reading efficiency. Meanwhile, plenty of thin-film magnetic heads are simultaneously formed from one wafer, however, the scaling precision of the edge portion may be deviated.